Basic compounds according to the invention are generally used in aqueous solution, but can also occur in the form of crystalline solids.
Said compounds are mainly used in the conditioning of water as flocculants and in the paper-sizing process. Bauxite, bayerite, gibbsite, hydrargillite etc. may be materials used as raw material, provided that they are hydrated oxides.
For the sake of simplicity, said compounds are hereinafter indicated by the generic term alumina.
Various methods, disclosed in patent and scientific literature, are known for obtaining basic compounds.
Ignoring electrochemical methods, the method most used industrially is the one which provides for the etching of alumina with a marked stoichiometric lack of hydrochloric acid. This etching must be performed at temperatures above 100.degree. C. and under pressure. This process, operating under pressure and with a large excess of alumina which must be recycled, requires technologically demanding systems.